By using squirrel monkeys (Saimiri sciureus) the locomotor equilibrium function, oculomotor function and morphology will be studied correlatively. Selective destruction of different areas of the body equilibrium system such as otolith end organ ablation or vestibular nucleus lesion will be performed. Locomotor equilibrium function will be studied by squirrel moneky rail test or squirrel monkey platform runway test which is based upon shuttle avoidance conditioning procedure. The functional measurements will provide quantitative and comparative data of body equilibrium function both pre- and post-ablation. Concommitent oculomotor investigation will be performed in order to compare the status of vestibulo-spinal and vestibulo-oculomotor functions. Statistical procedures will be used for data analysis. The morphological confirmation of ablative lesions will be performed both in the temporal bones and neurological specimens. The present study will provide contributory information toward the clinical diagnostics and also for the study of rehabilitation from many different disease conditions.